Three terminal SOT memory cell with anomalous Hall effect
View Patent ↗A method and apparatus for deterministically switching a free layer in a spin orbit torque magnetoresistive random access memory (SOT-MRAM) cell is disclosed herein. In one embodiment, an SOT-MRAM memory cell is provided. The SOT-MRAM memory cell includes a magnetic tunnel junction, a ferromagnetic bias layer, and an antiferromagnetic layer. The magnetic tunnel junction includes a free layer having primarily two bi-stable magnetization directions, a reference layer having a fixed magnetization direction, and an insulating tunnel barrier layer positioned between the free layer and the reference layer. The ferromagnetic bias layer is configured to provide spin orbit torque via anomalous Hall effect and simultaneously configured to provide a magnetic bias field on the free layer to achieve deterministic switching. The antiferromagnetic layer is positioned below the ferromagnetic bias layer and is configured to pin a magnetization direction of the ferromagnetic bias layer in a predetermined direction.
1. A spin orbit torque magnetoresistive random access memory (SOT-MRAM) cell, comprising:
a magnetic tunnel junction, comprising:
a free layer having primarily two bi-stable magnetization directions;
a reference layer having a fixed magnetization direction; and
an insulating tunnel barrier layer positioned between the free layer and the reference layer;
a ferromagnetic bias layer configured to provide spin orbit torque via anomalous Hall effect and simultaneously configured to provide a magnetic bias field on the free layer to achieve deterministic switching, wherein the ferromagnetic bias layer comprises tapered edges; and
an antiferromagnetic (AFM) layer positioned adjacent to the ferromagnetic bias layer, configured to pin a magnetization direction of the ferromagnetic bias layer in a pre-determined direction.
2. The SOT-MRAM cell of claim 1 , further comprising:
a conductive capping layer disposed on the AFM layer.
3. The SOT-MRAM cell of claim 1 , further comprising a nonmagnetic spin Hall effect layer.
4. The SOT-MRAM cell of claim 3 , wherein the spin Hall effect layer is formed from Pt, Ta, W, or copper doped with either bismuth or iridium, or combinations thereof.
5. The SOT-MRAM cell of claim 1 , wherein the tapered edges have a slope configured to provide additional knob to tune a strength of a stray field from the ferromagnetic bias layer to the free layer and a current density in the ferromagnetic bias layer.
6. The SOT-MRAM cell of claim 1 , wherein the ferromagnetic bias layer is milled.
7. A spin orbit torque magnetoresistive random access memory (SOT-MRAM) cell, comprising:
a magnetic free layer;
a ferromagnetic bias layer configured to produce an anomalous Hall effect to provide spin orbit torque, and simultaneously configured to provide a magnetic bias field to deterministically switch the free layer from a first magnetization state to a second magnetization state, wherein the ferromagnetic bias layer comprises tapered edges;
a spacer positioned between the free layer and the ferromagnetic bias layer to magnetically decouple the free layer from the ferromagnetic bias layer and to pass spin current from the ferromagnetic bias layer to the free layer; and
an antiferromagnetic layer positioned adjacent to the ferromagnetic bias layer, the antiferromagnetic layer configured to exchange pin a magnetization direction of the ferromagnetic bias layer.
8. The SOT-MRAM cell of claim 7 , further comprising:
a reference layer having a fixed magnetization direction; and
an insulating tunnel barrier layer positioned between the free layer and the reference layer, wherein the free layer, the tunnel barrier layer, and the reference layer are collectively a magnetic tunnel junction.
9. The SOT-MRAM cell of claim 7 , further comprising a non-magnetic spin Hall effect layer.
10. The SOT-MRAM cell of claim 9 , wherein the spin Hall effect layer is formed from Pt, Ta, W, or copper doped with either bismuth or iridium, or combinations thereof.
11. The SOT-MRAM cell of claim 7 , wherein the tapered edges have a slope configured to provide additional knob to tune a strength of a stray field from the ferromagnetic bias layer to the free layer and a current density in the ferromagnetic bias layer.
12. The SOT-MRAM cell of claim 7 , wherein the ferromagnetic bias layer is milled.
13. A spin orbit torque magnetoresistive random access memory (SOT-MRAM) cell, comprising: a magnetic tunnel junction, comprising: a free layer having primarily two bi-stable magnetization directions; a reference layer having a fixed magnetization direction; and an insulating tunnel barrier layer positioned between the free layer and the reference layer; a ferromagnetic bias layer configured to provide spin orbit torque via anomalous Hall effect and simultaneously configured to provide a magnetic bias field on the free layer to achieve deterministic switching; an antiferromagnetic (AFM) layer positioned adjacent to the ferromagnetic bias layer, configured to pin a magnetization direction of the ferromagnetic bias layer in a pre-determined direction; and a conductive capping layer disposed directly on and substantially covering an extended portion of the ferromagnetic bias layer.
14. The SOT-MRAM cell of claim 13 , further comprising a nonmagnetic spin Hall effect layer.
15. The SOT-MRAM cell of claim 14 , wherein the spin Hall effect layer is formed from Pt, Ta, W, or copper doped with either bismuth or iridium, or combinations thereof.
16. The SOT-MRAM cell of claim 13 , wherein the ferromagnetic bias layer is milled.